CN102816363A - High resilience flame retardant antistatic foamed polyethylene material - Google Patents

Abstract

The invention discloses a high-resilience flame-retardant antistatic foamed polyethylene material, comprising a foaming matrix, a foaming agent, a nucleating agent, a flame retardant, and an antistatic agent, wherein the flame retardant is mainly composed of a bromine-based flame retardant, and the antistatic agent is mainly composed of conductive carbon black. The high-resilience flame-retardant antistatic foamed polyethylene material is prepared by mixing, cross-linking, and molding the foaming matrix, the foaming agent, the nucleating agent, the flame retardant, and the antistatic agent. The high-resilience flame-retardant antistatic foamed polyethylene material not only has high resilience, but also has flame retardant and antistatic properties.

Description

High resilience flame retardant antistatic foamed polyethylene material

the

technical field

The invention relates to a foamed plastic, in particular to a high-rebound flame-retardant and antistatic foamed polyethylene material.

the

Background technique

Foam plastic is a porous material with plastic as the basic component and contains a large number of air bubbles. Foam plastics have many advantages, such as light weight, good thermal and sound insulation properties, high specific strength, ability to absorb impact loads, low price, and material saving. Therefore, foam plastics are widely used in many aspects of industry, agriculture, household appliances, transportation, military, aerospace and daily necessities.

According to the expansion ratio, foamed plastics can be divided into high foaming matrix and low foaming matrix; according to the physical properties of plastics, they can be divided into three categories: rigid foamed plastics, semi-rigid foamed plastics, and soft foamed plastics; Bubble structure is divided into open cell type and closed cell type. In closed-cell foam plastics, the air bubbles are dispersed in the polymer in isolation to form a dispersion, and the matrix polymer is a continuum. In open-cell foam, the bubbles in the polymer are broken, and the bubbles can be connected, so the gas phase in the foam and the polymer matrix are both continuous phases, and the fluid can pass through the foam. In the actual foam body, most of the cells are between the closed cells and the open cells.

With the continuous improvement of the performance requirements of foam plastics in special fields such as aviation, aerospace, and electronics, traditional foam plastics can no longer meet the special requirements of these fields for material strength, stiffness, heat resistance, flame retardancy, and antistatic. Therefore, high performance has become a new direction of foam research. At present, foreign countries have used high-performance foam plastics as load-bearing structural materials in aviation, aerospace, transportation and other fields, such as the skeleton of satellite solar cells, the fairing of the front end of rockets, the vertical tail of unmanned aircraft and the body of cruise missiles. Missile wings, large radome of ships, etc. The main ways to improve the performance of foamed plastics are: (1) to modify traditional foamed plastics with other materials to improve physical and chemical properties, or to improve the cells, foam structure and bubbles in the polymer through special foaming process conditions. (2) Develop a new type of foam with a more reasonable molecular chain structure.

There are many types of foamed plastics, the main ones are polyurethane (PU) soft and hard foaming products, polystyrene (PS) and polyethylene (PE) foaming products. Because PU foam products will leave traces of isocyanate harmful to human body, and PU product materials cannot be recycled. PS foam products use chlorofluorocarbons in the foaming process, which destroys the ozone layer of the earth's atmosphere; waste PS foam products will also cause "white pollution" to the surrounding environment. Compared with PS and PU foam products, PE foam products are favored by people for their excellent heat resistance, mechanical strength and good environmental adaptability.

Existing PE foam products have a large number of research and development reports and products coming out at home and abroad. The main foreign manufacturers include Japan's JSP, Germany's BASF and GEFINEX, Italy's AMUT, New Zealand's ULTRALON, Austria's PCD, and Denmark's BOREALIS , CSI in the United States, etc. The products of these grades have certain resilience properties, however, they are not flame retardant, nor are they antistatic products. Foamed PE products with high resilience, flame retardancy and antistatic properties have not been successfully developed so far.

the

Contents of the invention

In view of the above, the present invention provides a high resilience flame retardant antistatic foamed polyethylene material.

A high-resilience flame-retardant antistatic foamed polyethylene material, including a foaming matrix, a foaming agent, a nucleating agent, a flame retardant, and an antistatic agent. The main component of the flame retardant is a brominated flame retardant , the main component of the antistatic agent is conductive carbon black, and the high resilience flame retardant antistatic foamed polyethylene material is prepared by mixing the above foam matrix, foaming agent, nucleating agent, flame retardant Refined, cross-linked and molded.

The high-resilience flame-retardant and antistatic foamed polyethylene material of the present invention is mixed, cross-linked and Molded to obtain a foamed polyethylene material that is both highly resilient, flame retardant and antistatic.

the

Description of drawings

Fig. 1 is a flow chart of the forming process of high resilience flame retardant and antistatic foamed polyethylene material according to the preferred embodiment of the present invention.

the

Detailed ways

In order to describe the technical content, structural features, achieved goals and effects of the present invention in detail, the following will be described in detail in conjunction with the embodiments and accompanying drawings.

A preferred embodiment of the present invention discloses a high-resilience flame-retardant antistatic foamed polyethylene material, including a foaming matrix, a foaming agent, a nucleating agent, a crosslinking agent, a foaming accelerator, a flame retardant, and an antistatic Static agent, the flame retardant is a brominated flame retardant, the main component of the antistatic agent is conductive carbon black, and the high resilience flame retardant antistatic foamed polyethylene material is obtained by mixing, crosslinking and Molded.

In order to make the prepared foamed polyethylene material have high resilience, the foamed matrix as the matrix material of the foamed polyethylene material must have high resilience, and pure polyethylene (PE) as the foamed matrix has low elasticity and is difficult to adapt to Packaging, shoemaking and many other industries require different rubber or thermoplastic elastomers to improve the performance of polyethylene (PE). It will be screened according to the principles of polarity (molecular structure), solubility parameter, surface tension, viscosity (molecular weight and its distribution) and crystallinity, mainly polybutadiene rubber (BR), vinyl acetate copolymer (EVA ), EPDM, styrene-butadiene-styrene block copolymer (SBS), natural rubber (NR), etc. Polyethylene and vinyl acetate copolymer (EVA) has good flexibility, and its elasticity varies with the content of VA (vinyl acetate). Using EVA with a VA content greater than 20% can greatly improve the resilience of low-density polyethylene (LDPE). Since EVA is more expensive, other substances can also be used to improve the resilience of LDPE. Styrene-butadiene-styrene block copolymer (SBS) copolymer is a thermoplastic elastomer, and the use of SBS to modify LDPE can significantly improve the impact elasticity and compression recovery rate of the foamed matrix. Using polybutadiene rubber (BR), natural rubber (NR) and styrene-butadiene rubber (SBR) to modify LDPE not only improves the impact elasticity of the foam matrix, but also reduces the sensitivity of the foam material to temperature, which is beneficial Scale up the production of foamed substrates. A new type of LDPE modifier has been found in the existing literature. The PR series chlorinated polyethylene (CPE) is used as a modifier by chlorination of waste PE agricultural film. Due to the introduction of polar group chlorine on the PE macromolecular chain and the In the presence of oxidized groups, a foaming matrix with good comprehensive properties can be obtained by adding it to LDPE. In this preferred embodiment, the main components of the foam matrix are low-density polyethylene (LDPE) and vinyl acetate copolymer (EVA), which have high resilience.

The blowing agent is used to generate air bubbles in the foam matrix. There are three methods for forming cells of existing PE foam products: mechanical foaming, physical foaming and chemical foaming. Mechanical foaming is to use strong mechanical stirring to make the gas evenly distributed in the resin and form bubbles. Physical foaming is to change the physical state in the resin by means of a blowing agent to form a large number of bubbles. The above two processes are completely physical processes without any chemical changes. Chemical foaming means that during the foaming process, the chemical foaming agent undergoes a chemical reaction to generate gas and form cells in the resin. Common physical blowing agents are: pentane, isopentane, hexane, isohexane, propane, butane, dichloromethane, dichlorotetrafluoroethane F114, dichlorotetrafluoromethane F11, trichlorodifluoroethane F112, dichlorodifluoromethane F12. The first six low-boiling blowing agents are low in price and low in toxicity, but their disadvantages are that they are flammable and explosive, which is extremely unfavorable to processing. Dichloromethane is poisonous; the last four freons, though non-toxic and good flame retardancy, will destroy the ozone layer of the atmosphere and damage the earth's environment. At the same time, physical foaming and mechanical foaming have high requirements on equipment, and the utilization rate of foaming agent is low. Therefore, the preparation of the PE foamed product in the present invention selects the chemical foaming method. There are many types of chemical blowing agents, which can generally be divided into two categories: organic and inorganic.

Inorganic chemical foaming agents mainly include sodium bicarbonate and ammonium carbonate. The industrial use of inorganic chemical foaming agents to produce foamed polyolefins is less, because such foaming agents are not easy to disperse in polymers, and the temperature range of decomposing and releasing gas is relatively wide, which is not easy to control; the carbon dioxide gas produced is easy to pass through The membrane wall dissipates, so this type of inorganic chemical blowing agent is often used as an auxiliary blowing agent. Organic chemical foaming agent is the main foaming agent for polymer chemical foaming. The main advantages are good dispersion in resin and narrow decomposition temperature range. There are more than a dozen commonly used organic chemical foaming agents, mainly azo, nitroso and sulfonyl hydrazide compounds, among which azodicarbonamide (AC) is cheap, and its decomposition products are non-toxic and odorless , colorless, high decomposition temperature, easy to store, large amount of gas generation, is a high-efficiency foaming agent. In this preferred embodiment, the main component of the blowing agent is azodicarbonamide (AC).

The nucleating agent is used to form bubble nuclei. Both physical foaming and chemical foaming involve the formation of bubble nuclei. Fillers of tiny crystals are commonly used as nucleating agents, such as dibenzylidene sorbitol (DBS), etc., which can promote the formation of bubbles in polymer melts. Some inorganic additives that are not compatible with the resin can also act as nucleating agents in the polymer. In the process of cell formation, when the gas is released from the polymer melt, bubbles are formed with tiny crystals as nuclei, and each bubble is closed by the liquid phase of the incompatible polymer melt, so that the bubbles rarely gather , to avoid bubbles communicating to form large pores.

The crosslinking agent is used to improve the viscoelasticity of the molten polyethylene (PE) after melting. Since polyethylene (PE) is a crystalline polymer, when heated to the melting point, the viscosity drops sharply, which is extremely unfavorable for foam molding. Because foam molding requires the polymer melt to have suitable viscoelasticity to keep the gas and form isolated bubbles. If the PE melt has the viscoelasticity required to adapt to foaming, it must be controlled within a narrow temperature range, and it is difficult to control the foaming molding process. At the same time, N ₂ , CO ₂ , CO and other gases decomposed by the chemical blowing agent have a large permeability coefficient in the PE melt, and the bubbles are easy to escape. For this reason, an appropriate amount of cross-linking agent must be added during polyethylene foam molding, so that the molecular chains of the polymer are cross-linked after melting, free radicals are generated on the polymer macromolecular chains, and then cross-linked with each other to form a molecular chain network structure. Thereby increasing the viscoelasticity of the melt and broadening the temperature range of the PE melt suitable for foam molding. When selecting a cross-linking agent, it must be satisfied that (1) the decomposition temperature of the cross-linking agent must be higher than the melting point of PE and lower than the decomposition temperature of the blowing agent; (2) the degree of cross-linking required for PE foaming must be met. Considering the above factors and cost factors, in a preferred embodiment of the present invention, dicumyl peroxide (DCP) is selected as the cross-linking agent of PE.

However, due to the higher decomposition temperature of AC foaming agent, the temperature of a large amount of decomposition reaches 190-210°C, while the decomposition temperature of DCP is 150-170°C, so the temperature difference between the two is 20-60°C. That is to say, after DCP has been completely decomposed, PE cross-linking is completed, and the macromolecular chain has formed a network structure, AC begins to decompose. If the cross-linking is excessive, the melt viscosity will be too high, and the expansion of bubbles will be inhibited, which is not conducive to the preparation of high-resilience and high-foaming products. Therefore, a foam accelerator must be introduced to reduce the decomposition temperature of AC. Suitable AC foam accelerators include zinc oxide, zinc stearate, barium stearate, urea, zinc carbonate, biurea, borax, hexanolamine, cadmium oxide, etc.

The flame retardant is used to improve the flame retardancy of the foamed polyethylene material, that is, it is not easy to burn. The combustion performance of the foamed material includes the flammability, ignition temperature, calorific value, smoke, thermal decomposition and the type of gas generated after combustion of the foamed material, which are related to the composition of the foamed plastic, the expansion ratio and the cell structure related. There are only two elements of carbon and hydrogen in the PE molecular chain, and its own limiting oxygen index is very low, only 17.4, which is extremely flammable; and as the material density decreases, foamed PE is more flammable, and foamed PE is used in refrigeration and air conditioning ducts. It is used as a building interior material in the fields of heating, heating and heat preservation. Therefore, it is very necessary to improve the flame retardancy of foamed PE. Existing flame retardants include halogen-free flame retardants and halogen-containing flame retardants. Brominated flame retardants have excellent flame retardant properties on PE, and the flame retardant effect is remarkable. In this preferred embodiment, brominated flame retardants are used as flame retardants, supplemented with organosilicon flame retardant synergists to improve flame retardant performance. Effect.

The antistatic agent is used to improve the conductivity of the foamed polyethylene material. Usually, the antistatic improvement of foamed PE materials is mainly to form a conductive layer on the surface of the product by electroplating, coating, impregnation, etc. to increase its surface conductivity. Due to the limitations of product characteristics, coating antistatic agents also have fatal defects such as poor durability, which is mainly due to the fact that the coating of antistatic agents is easy to fall off due to friction and washing during use. The conductivity of the foamed polyethylene material in the invention is improved by adding an antistatic agent to PE. Described antistatic agent comprises conductive carbon black, graphite, metal powder, ATO (being SnO2+Sb2O3), polyaniline etc., antistatic agent mainly adopts conductive carbon black in this preferred embodiment, adds other antistatic agent composite .

There are many ways to produce foamed polyethylene materials by using the above ingredients, such as extrusion foaming, molded foaming, injection foaming, rotational molding foaming, solution coating foaming, etc. Extrusion molding is a process of foam plastic molding. One of the main methods, due to the continuity of the extrusion molding method, the extrusion molding method is generally used for foaming products such as profiled materials, plates, pipes, diaphragms, and cable insulation layers, which dominates the production of PE low-foaming products. . There are two basic processes of extrusion foaming: free foaming process and controlled foaming process. The disadvantage of the former is that it does not control the matching of melt pressure and gas dissolving power, and it is difficult to obtain low density and smooth and uniform outer skin. The latter utilizes the basic principle of the "Seluka" method to control the density of the product and obtain a crust with a lower foaming ratio. The former is often limited to the production of products with a smaller area, while the latter can be used for the production of products with larger cross-sections, but the cost is higher. The main disadvantage of extrusion foam molding is that it is not suitable for the production of PE products with complex shapes and high foaming, and the required production equipment is also relatively complicated.

Compression foam molding is a method in which a foamable material is placed in a mold and heated and pressurized to make it foamed. It can be used to form low-density structural foam plastics, and can also be used to form high-expansion ratio foam plastics, and can produce large-area, thick-walled or multi-layer foam plastics. Polyethylene foam compression molding is divided into one-step method and two-step method according to the foaming method. The foaming process of one-step molding is completed at one time, and the specific molding process includes: batching, mixing, molding, crosslinking, and foaming. The basic procedure of the two-step foaming method of PE molding is the same as that of the one-step method, except that after the cross-linking is completed, a part of the foaming agent is decomposed, and the material is partially foamed, let it cool down, or carry out the second step under normal pressure while it is hot. Second heating foaming. Because the material expansion rate of the two-step foaming method is greatly reduced, the foaming ratio can be increased, up to 30 times, and the thickness of the plate can reach 100 mm.

The main feature of the injection foam molding is one-time molding, which greatly simplifies the manufacturing process of foam products. The product quality is good and the output is high, especially for foam plastic products with complex shapes and high size requirements, which can show its superiority. . The disadvantage is that the requirements for the mold are high, and the products are mostly low-foaming products. The injection foam molding process consists of raw material preparation, plasticization and metering, mold closing, injection, foaming, cooling and setting, mold opening and ejection of products, and product processing. There are three main factors affecting the injection molding process: pressure, temperature and time. In order to improve the quality of the product, the three elements must match each other.

Referring to Fig. 1, when the present invention makes high-resilience flame-retardant and antistatic foamed polyethylene materials, the main components of the foaming matrix in this embodiment are LDPE and EVA, the main components of the foaming agent are AC, and the nucleating agent is common The main component of the crosslinking agent is DCP, the main component of the foaming accelerator is zinc oxide, the main component of the flame retardant is brominated flame retardant, and the main component of the antistatic agent is conductive carbon black. During production, LDPE, EVA and various other components are put into the extruder for high-speed mixing, heated and extruded into a sheet masterbatch, and then chemically cross-linked to form a foaming material, and then molded once or twice to form foamed PE, Forming, post-processing, winding and other processes to make a coil of foamed polyethylene material.

It is worth pointing out that when using a cross-linking agent to carry out the cross-linking reaction of the polymer, the increasing melt viscosity makes the dispersion of the cross-linking agent in the polymer matrix worse, resulting in uneven cross-linking and local occurrence of "scorch". burn" phenomenon. The decomposition temperature of the peroxide crosslinking agent is close to the melting temperature of the polymer, and the loss of peroxide is inevitable during processing, which makes it difficult to control the degree of crosslinking. According to the above, the present invention also has another method for manufacturing foamed polyethylene materials, which uses radiation crosslinking, that is, through high-energy rays, such as gamma rays or electron rays, to make PE produce macromolecular free radicals, and the free radicals Termination of the double-radical coupling occurs and chemical bonds are formed to cross-link the macromolecular chains. In this way, there is no need to use crosslinking agents and foaming accelerators, which ensures the cleanliness of the material and improves the electrical insulation of PE. Radiation sources for radiation crosslinking include gamma radiation sources of radioactive elements and electron accelerators, of which there are two types of gamma radiation sources: 60Co and 137Cs. The cross-linked network of the product cross-linked by radiation is evenly distributed, the quality is easy to control, the scrap rate is low, and the production efficiency is high. In addition, PE can significantly improve its heat resistance, corrosion resistance, and crack resistance through radiation crosslinking, and its insulation and mechanical properties are also significantly improved.

The above is only an embodiment of the present invention, and does not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made by using the description of the present invention and the contents of the accompanying drawings, or directly or indirectly used in other related technologies fields, all of which are equally included in the scope of patent protection of the present invention.

Claims (10)

1. A high-resilience flame-retardant and antistatic foamed polyethylene material, including a foaming matrix, a foaming agent, and a nucleating agent, is characterized in that: the foamed polyethylene material also includes a flame retardant and an antistatic agent , the main component of the flame retardant is a brominated flame retardant, the main component of the antistatic agent is conductive carbon black, and the high resilience flame retardant antistatic foamed polyethylene material agent, nucleating agent, flame retardant, antistatic agent mixing, cross-linking, molding. 2. The foamed polyethylene material according to claim 1, characterized in that: the main components of the foamed matrix are polyethylene (PE) and the following polybutadiene rubber (BR), vinyl acetate copolymer (EVA), EPDM, styrene-butadiene-styrene block copolymer (SBS), natural rubber (NR). 3. The foamed polyethylene material according to claim 1, characterized in that: the main component of the foaming agent is azodicarbonamide (AC). 4. The foamed polyethylene material according to claim 1, characterized in that: the foamed polyethylene material further comprises a cross-linking agent, and the main component of the cross-linking agent is dicumyl oxide (DCP). 5. foamed polyethylene material according to claim 4, is characterized in that: described foamed polyethylene material further comprises foam accelerator, and foam accelerator is zinc oxide, zinc stearate, barium stearate , urea, zinc carbonate, biurea, borax, hexanolamine, cadmium oxide or any combination thereof. 6. The foamed polyethylene material according to claim 1, characterized in that: the main component of the nucleating agent is dibenzylidene sorbitol (DBS). 7. The foamed polyethylene material according to claim 1, characterized in that: said antistatic agent also includes graphite, metal powder, ATO, polyaniline. 8. The foamed polyethylene material according to claim 1, characterized in that: the flame retardant also includes a silicone-based flame retardant synergist. 9. The foamed polyethylene material according to claim 5, characterized in that: said cross-linking is chemical cross-linking by adding said cross-linking agent and a foaming accelerator. 10. The foamed polyethylene material according to claim 1, characterized in that: the cross-linking method adopts a radiation cross-linking method, and high-energy rays cause PE to generate macromolecular free radicals.

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